ATOMIC ABSORPTION SPETROSCOPY

ATOMIC ABSORPTION BY

ABDUL QAYOOM MUGHERI

M,phil scholar

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Atomic Absorption Spectroscopy

Introduction Atomic absorption spectroscopy is an analytical technique for determining the concentration of a particular metal element in a sample.

This technique can be used to analyze the concentration of over 70 different metals in a solution.

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Background

Atomic absorption spectrometry was first used as an analytical technique. It was established in the second half of the 19th century.

The modern form of AAS was largely developed during the 1950s by Sir Alan Walsh

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Atomic Energy Level Diagrams

we should be aware that only valence electrons are responsible for atomic spectra observed in a process of absorption or emission . Valence electrons in their ground states are assumed to have an energy equal to zero . As an electron is excited to a higher energy level, it will absorb energy exactly equal to the energy difference between the two states.

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Atomic Emission and Absorption Spectra

At room temperature, essentially all atoms are in the ground state. When they absorb energy they excited. Excited electrons will only spend a short time in the excited state an excited electron will emit a photon and return to the ground state.

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The Effect of Temperature on Atomic Spectra

Atomic spectroscopic methods require the conversion of atoms to the gaseous state. This requires the use of high temperatures (in the range from 2000-6000 oC). The high temperature can be provided through a flame, electrical heating.

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The original 1954 AAS instrument

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Atomic absorption spectrophotometer consists of a light source, a sample

compartment and a detector.

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- Atomic absorption is a very common technique for detecting metals and metalloids in environmental samples.

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Elements detectable by atomic absorption are highlighted in pink in this periodic table

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Atomic Absorption Spectrometer

• Atomic absorption spectrometers have 4 principal components

1 - A light source ( usually a hollow cathode lamp )

2 – An atom cell ( atomizer )

3 - A monochromator

4 - A detector , and read out device .

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Schematic diagram of AAS

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ATOMIZATION

Elements to be analyzed needs to be in atomic state.

Atomization is the separation of particles into individual molecules and breaking molecules into atoms .This is done by exposing the analyte to high temperature in a flame or graphite furnace .

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There are two types of atomization

A. Flame B. Graphite furnace atomization .

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FLAME

Flame AA can only analyze solutions , where

path length, and therefore to increase the total absorbance .

Sample solutions are usually introduced into a nebuliser , which can be readily broken down in the flame.

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TYPES OF FLAME

The common fuels and oxidants employed in flame spectroscopy and the approximate range of temperature realized with each of these mixtures.

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The process by which the energy of the light (in the form of photons) is transferred to the atoms or molecules raising them from the ground state to an excited state ,that absorbed radiations are characteristics for each element.

ABSORPTION SYSTEM

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The Atomic Absorption Spectrometer Sample Introduction System

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Nebuliser

Capillary

Solution

A mechanical device that burns a gas or liquid fuel into a flame in a controlled manner

TYPES OF BURNER

Premix chamber burner

Total consumption burner

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PREMIX BURNER

Most commonly use premix burner the oxidant-sample mixture flows into a chamber located upstream from the flame, where the larger drops are separated from the mixture and discarded.

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Importance of Flame in Atomization

A Flame burning in air forms an ideal means for converting a Solution into the atomic vapor required for atomic absorption

A flame is simple, inexpensive & easy to use

A flame provides a remarkably stable environment for atomic absorption

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GRAPHITE FURNACE

The graphite furnace has several advantages over a flame. First it accept solutions or solid samples.

Samples are placed directly in the graphite furnace and the furnace is electrically heated in several steps to dry the sample, ash organic matter, and vaporize the analyte atoms.

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Advantages Over AAS

Solutions and solid samples can be analyzed. Much more efficient atomization Greater sensitivity Smaller quantities of sample (typically 1-

100µL)

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Disadvantages

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Expensive low precision low sample throughput requires high level of operator skill

ACKNOWLEDGEMENT

I am thankful to Almighty Allah,

prof. Dr. Tasneem Gul kazi And also thankful to my classmates for wonderful cooperation.

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